Magnetic materials are commercially important, and a commercial need exists to develop smaller magnetic structures, approaching single domain sizes. Processing of magnetic materials, however, can be a challenge, particularly at smaller scales. For example, high temperature may be needed for fabrication which could prevent some applications or increase production cost. Hence, a commercial need exists to find better methods to fabricate smaller magnetic structures. In addition, a commercial need exists to better understand how magnetic behavior is a function of structure size. For example, the coercivity of small particles can depend on particle size. At smaller sizes, moreover, interfacial surface effects generally become more significant. Layering of magnetic structures can be significant, including the GMR effect (giant magnetoresistance effect). Many applications are important for small magnetic structures including high-density recording media, nonvolatile memories, microwave circuits, biosensors, bioelectronics, communication devices, and magnetic microscopy.
Types of magnets include soft magnets and hard magnets. In particular, hard magnets are of commercial interest which generally have high permanent magnetization, high coercivity (e.g., Hc greater than or equal to about 10 Oe), and high mechanical and chemical stability. Generally, hard magnets, which are a type of permanent magnet, display a relatively squarish magnetization v. field (M-H) loop, coupled with physical and chemical stability. For example, they can be useful permanent magnets which are difficult to demagnetize by unexpected fields. One important example of a hard magnet is barium hexaferrite (BaFe). Like many magnetic materials, however, BaFe, can be difficult to pattern at higher resolution. Thin film preparation can be carried out using rf sputtering, or reactive magnetron sputtering, followed by annealing at high temperature. Some of the resultant thin film can be nonmagnetic. In addition, a need exists to reduce the grain size.
Small magnetic structures, in principle at least, can be patterned by electron beam lithography, but this method requires expensive instrumentation and is not very versatile. For example, the electron beam can introduce chemical changes to the materials upon exposure and requires a high vacuum.
Improved methods are needed to pattern small magnetic structures including nanostructures. The methods should be convenient, versatile, and provide high resolution and alignment. Methods should be applicable to magnetic materials which are difficult to process.